1. Field of the Invention
This invention relates to lathe chucks and in particular to a four-jaw lathe chuck having means for coordinating and interrelating the positions of various combinations of the jaws of a lathe chuck.
2. Description of the Prior Art
Conventional four-jaw lathe chucks require a relatively long setup time for the operator to center the workpiece. This setup time is a significant part of the total time for performing a lathing operation. With a conventional four-jaw chuck the setup of the workpiece is a complicated, inexact task. After measuring the initial off-center position of the workpiece, the appropriate jaw is tightened to move the workpiece inward a random distance at the most out of center point after the opposite jaw is backed off an equal distance. Thus, the workpiece is pressed closer to the center position. This process is repeated until the workpiece appears centered. Often however, the off center axis of the workpiece does not coincide with the axis of either pair of opposed jaws. This leads to a lengthy sequence of inconclusive approximations to adequately center a piece of material secured in the jaws for machining.
A further drawback of the conventional four-jaw chuck is the difficulty in repeating the centering operation just described when a substantial number of identical pieces are to be machined. Each successive piece has to be centered all over again.
For simple cylindrical workpieces the conventional three jaw "universal" chuck is much faster. The three jaws converge in unison and grip around workpiece in a centered position in relation to the chuck axis. While it is a relatively simple matter to center cylindrical workpieces, a three-jaw chuck is rarely used for other than cylindrically shaped workpieces. Further, the accuracy of three-jaw chucks is at a maximum when the chuck is new, since all three jaws are usually actuated by the same spiral thread on a chuck plate.